Rodent bedding may contain compounds that affect the same endpoints that are the target of NTP's testing program, such as reproduction and development. For example, endotoxins (a byproduct of mold) can mask responses to exposure to asthma-causing agents. We are working with the Quality Assurance Laboratory to quantify these effects and develop guidelines for limits on contaminants in bedding of rodent studies. The ability of acrylamide, a compound found in heated cooking oils, to interfere with reproduction in rodents has been well-established. We fed male mice diets containing either 10% fat or 60% fat, creating groups of lean or obese male mice, respectively. We then showed that obesity in male mice greatly exacerbated the reproductive toxicity of acrylamide. Obese males exposed to acrylamide produced fewer and smaller litters than males that were lean and exposed to acrylamide or that were obese or lean and not exposed to acrylamide. We contributed to the study design of a multi-strain mouse study in which different strains are exposed to ionizing radiation then followed up for development of tumors. These strains were selected to represent a broad range of genetic variation. Although the data are not yet complete, the early indications are that different strains have a range of susceptibility to radiation and show varying locations and rates of tumors.